Method of producing crosslinked polyethylene stretched film

Abstract

An oriented film is prepared by crosslinking a sheet of polyethylene (preferably HDPE) containing particulate inorganic slip and antiblock additions to provide maximum crosslinking at the surfaces of the sheet and minimum orientation at its middle layer portion, and thereafter heating and stretching the film to obtain an oriented HDPE of high clarity film of improved moisture proof.

What is claimed is: 
     
       1. A method for producing high clarity oriented polyethylene film which comprises (a) crosslinking opposite surfaces of a sheet of polyethylene having a density greater than 0.935 and containing from 0.02 to 1 parts by weight per 100 parts by weight of said polyethylene of a particulate inorganic compound selected from the group consisting of zeolite, silica, alumina, and bentonite, having an average particle size less than 20 microns, said crosslinking produces gel fractions in opposite outer layer portions of the sheet of between 20% and 70% and a gel fraction in a middle layer portion of the sheet of between 0 and 5%,   (b) heating and stretching the crosslinked sheet under conditions to orient the polyethylene molecules thereby producing an oriented film.   
     
     
       2. The method as defined in claim 1 wherein the polyethylene is HDPE. 
     
     
       3. The method as defined in claim 1 wherein the outer layer portions are crosslinked film and the middle layer portion is an uncrosslinked film, and the thickness ratio of the outer layer portion:middle layer portion:outer layer portion thereof ranging between 1:0.1:1 to 1:10:1. 
     
     
       4. The method as defined in claim 1 wherein the sheet is crosslinked by irradiating both surfaces of said sheet. 
     
     
       5. The method as defined in claim 1 wherein the sheet comprises crosslinked layers coextruded onto an uncrosslinked middle layer. 
     
     
       6. The method as defined in claim 3 wherein the sheet has a thickness of from 210 to 2000 microns and the stretching at least in one direction is at least 300 percent. 
     
     
       7. The method as defined in claim 1 wherein the crosslinking is carried out in an inert environment.